The present invention relates to the diagnosis and treatment of prostate cancer, and more specifically, to novel nucleic acid molecules, proteins and antibodies immunologically specific therefore which may be used to advantage for the diagnosis and treatment of prostate cancer.
Several publications are referenced in this application by author name and year of publication in parentheses in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these publications is incorporated by reference herein.
The molecular basis of cancer has been the subject of a massive research effort over the past several years. Through this effort, it has been discovered that abnormal cellular proliferation results not only from activation of oncogenes, but from disruption of certain genes whose function appears to be important in maintaining normal cell division. As a well-known example, mutations in the p53 tumor suppressor gene are common in human cancer and have been detected in tumor types from many different tissue sources.
This year prostate cancer is expected to be diagnosed in approximately 200,000 men in the U.S. and to result in the loss of 38,000 lives. Such numbers make prostate cancer the most frequently diagnosed malignancy (other than that of the skin) in American males and the second leading cause of cancer-related death in that group. Physicians usually detect cancers by finding a lump in the prostate gland, which is a walnut shaped structure that helps to maintain the viability of sperm. Such lumps may be discovered during a routine checkup or during examinations prompted by a patient""s complaint of sudden urinary discomfort or occasional impotence.
In some instances, prostate cancer is detected in the course of treatment for a disorder called benign prostatic hyperplasia. This condition, an aging-related enlargement of the prostate, affects more than half of all men older than 45 and gives rise (albeit more gradually) to the same urinary troubles caused by a prostate tumor. If the symptoms become too troublesome, a transurethral resection of the prostate, a process whereby parts of the gland are scraped away, may be performed. Whenever resection is done, the excised tissue is analyzed under a microscope for evidence of malignancy, which is occasionally found.
A simple blood test for prostate specific antigen (PSA) constitutes a third means of detecting prostate cancer. Increased PSA levels can signal the presence of cancer in individuals who display no symptoms of prostate abnormalities.
Prostate cancer is a disease with marked heterogeneity. Although many genes have been identified which are associated with the carcinogenesis of the prostate (Lara et al., 1999; Sciavolino and Abate-Shen, 1998), the mechanism underlying the development of prostate cancer is still poorly understood. However, it is believed to be a multi-step process that involves genetic alterations of genes controlling cellular proliferation, differentiation and programmed cell death. Deletion or down-regulation of these tumor suppressor genes often leads to the development of cancer.
To further understand the biological processes underlying the development of prostate cancer, the present inventors have identified a tumor suppressor gene which is expressed in normal but not malignant prostate tissue. Thus, in accordance with the present invention, novel biological molecules useful for identification, detection, and/or molecular characterization of components involved in the regulation of cellular differentiation and tumorigenesis are provided.
In a preferred embodiment of the invention, an isolated nucleic acid molecule is provided which encodes the human PTX1 protein. In a particularly preferred embodiment, the human PTX1 protein has an amino acid sequence comprising the sequence of SEQ ID NO:2. An exemplary PTX1 nucleic acid molecule of the invention comprises the sequence of SEQ ID NO:1.
According to another aspect of the present invention, an isolated nucleic acid molecule is provided, which has a sequence selected from the group consisting of: (1) SEQ ID NO: 1; (2) a sequence specifically hybridizing with preselected portions or all of the complementary strand of SEQ ID NO: 1; (3) a sequence comprising preselected portions of SEQ ID NO:1, (4) a complement of SEQ ID NO: 1, and (5) a sequence encoding part or all of a polypeptide comprising the sequence of SEQ ID NO: 2. Such partial sequences are useful as probes to identify and isolate homologues of the PTX1 gene of the invention. Accordingly, isolated nucleic acid sequences encoding natural allelic variants of the nucleic acids of SEQ ID NO: 1 are also contemplated to be within the scope of the present invention. The term natural allelic variants will be defined hereinbelow.
Host cells comprising the PTX1-encoding nucleic acids of the invention are also contemplated to be within the scope of the present invention. Such host cells include but are not limited to bacterial cells, fungal cells, yeast cells, plant cells, insect cells and other animal cells. The PTX1-encoding nucleic acids may be conveniently cloned into a plasmid or retroviral vector for introduction into host cells. Such cells are useful in screening methods to identify compounds which modulate PTX1 expression. Compounds so identified may have therapeutic value in the treatment of prostate cancer.
According to another aspect of the present invention, an isolated human PTX1 protein is provided. The loss of expression of this PTX1 protein correlates with the deregulated growth of prostate carcinomas.
In a preferred embodiment of the invention, the protein is of human origin, and comprises the amino acid sequence of SEQ ID NO: 2. In a further embodiment, the protein may be encoded by natural allelic variants of SEQ ID NO: 1. Inasmuch as certain amino acid variations may be present in human PTX1 protein encoded by natural allelic variants, such proteins are also contemplated to be within the scope of the invention. Antibodies immunologically specific for the human PTX1 protein described hereinabove are also provided.
In yet another aspect of the invention, methods are provided for genetic screening and diagnostic evaluation of patients at risk for, or currently suffering from, cancer of the prostate. The hybridization specificity of the nucleic acids of the invention may be used to advantage for differential evaluation of patients presenting with phenotypic characteristics common to prostate cancer. In a preferred embodiment of the invention, a method for identifying a mutation in a nucleic acid sequence in a patient sample is provided. This method comprises isolating a nucleic acid sample from a patient, contacting the nucleic acid sample with a nucleic acid sequence of SEQ ID NO: 1 under low stringency hybridization conditions to allow DNA duplexes to form between sequences of sufficient complementarity, isolating the DNA duplexes and assessing the duplexes for mismatched base pairing.
In another embodiment, the nucleic acid molecules of the invention may be used as diagnostic hybridization probes or as primers for diagnostic PCR analysis for PTX1 or mutations thereof. Antisense molecules are also provided herein and may be useful in the regulation of PTX1 expression. Other methods encompassed by the present invention include immunodetection methods for assessing biological samples for the presence of PTX1 proteins.
According to another aspect of the invention, a method is provided for identifying agents which modulate PTX1 activity. This method comprises contacting cells expressing PTX1 with an agent suspected of being able to modulate PTX1 activity, measuring proliferation of the cells expressing PTX1 in both the presence and absence of the agent and comparing the proliferation of cells expressing PTX1 in the absence of the agent and in the presence of the agent. An alteration in cell proliferation in the presence of the agent is indicative of the agent""s ability to modulate PTX1 activity.
In yet another embodiment of the invention, kits are provided for detecting PTX1 expression associated with a susceptibility to cancer. Such kits may be used to advantage to diagnose human prostate cancer.